(1) Field of the Invention
The present invention relates to a color picture tube of shadow mask type and, more specially to an assembly of a shadow mask frame with an inner shield for a more improved color cathode ray tube to easily couple the shadow mask frame with the inner shield.
(2) Description of the Related Art
FIG. 3 schematically depicts the internal structure of a face panel for a color picture tube of a general shadow mask type. A shadow mask frame 2 is disposed therein by an appropriate tool. A shadow mask 6 having a plurality of apertures through which electron beams pass are formed facing the face panel of the frame 2. Also, an inner shield 8 for shielding the influence of geomagnetic field over the electron beams injected from electron guns is fixed distant from the face panel of the frame 2 by a clip 10.
The way to couple the conventional frame 2 with the inner shield 8 is in detail described in FIG. 4.
The frame 2 has a rim part 12 and a flange part 14 which is bent nearly perpendicular to the rim part 12 and extended to the inside of the frame itself. The inner shield 8 has a fixing part 24 superposed on a flange part 14 of the frame and a shielding part 16 extending in an acute angle bent from the outer edge of the fixing part 24. The terms, "inner" and "outer" (edges) indicates the direction relative to the center of the frame.
The assembly of the frame 2 with the inner shield 8 is performed by the known clip 10. When superposing the flange part 14 of the shadow mask frame 2 on the fixing part 24 of the inner shield 8, a plurality of slots 18, 20 of the same shape which the clip 10 is inserted into are formed at a position where the flange part 14 is aligned with the fixing part 24 with each other.
In the assembling process, after adjusting the relative position of the frame 2 and the inner shield 8, so that slots 18, 20 of these members agree to each other, the clip 10 is then inserted into the slots 18, 20.
However, the free end of the fixing part 24 of the inner shield 8 and that of the flange part 14 of the frame 2 are extended in the same direction with each other. The working space in the vicinity of the slots 18, 20 is too small to insert the clip 10 thereto.
If the free end of the fixing part 24 of the inner shield 8 is extended to the direction opposite to the free end of the flange part of the frame 2, the working space in the vicinity of the slots 18, 20 may be enlarged. However, while this case can be generally applied to a color cathode ray tube of less than 16 inches, it can not be applied to the comparative large color cathode ray tube of more than 19 inches.
To solve this problem, a relatively large opening 22 is formed in the vicinity of the slots 20 of the inner shield 8.
In the assembling process of the frame 2 with the inner shield 8, the opening 22 serves a passage for insertion of the clip into the slots 18, 20.
If the opening is formed in the shield part 16, the shielding effect of the geomagnetic field obtained from the shield part 16 is reduced. Further, the inner shield is made of a thin steal sheet to a thickness of about 0.2 mm. The inner periphery edge of the opening 22 is so sharp as to do an injury to a worker.
U.S. Pat. No. 3,737,703 granted to Tokyo Shibaura electronic company of Japan discloses an invention entitled "Shadow mask frame structure" where the bending angle between the rim and the flange is formed with an obtuse angle.
However, an object of the above prior art technology is not to easily couple the frame with the inner shield but to prevent the torsional deformation of the frame appeared in the high temperature treatment during the forming process of the frame. This structure cannot overcome the difficulty in the assembling process of the frame with the inner shield.